Low NOx Gas Burners With Carryover Ignition

ABSTRACT

A gas burner for low NOx gas furnaces is disclosed with improved flame carryover for igniting one or more adjacent burners. The burner includes a burner tube that receives a mixture of fuel and air. The burner tube is coupled to an outlet. The outlet includes a primary outlet opening which is in communication with at least one transverse slot for communicating a flame to at least one adjacent burner. The primary outlet opening may be elliptical and the outlet further may also include a concave outer face through which the primary outlet opening extends. The at least one slot may include a pair of oppositely directed transverse slots extending outward from the primary outlet opening along a semi-minor axis of the primary outlet opening.

BACKGROUND

1. Technical Field

This disclosure relates to gas burners in general, and morespecifically, to gas burners of multi-burner applications where only oneburner contains an igniter and the remaining burners must be lit fromthe single burner with the igniter using flame carryover. Still morespecifically, this disclosure relates to improvements in flame carryoveraspects of low NO_(x) burners that reduce the gas used for flamecarryover while still providing a robust ignition for all burners.

2. Description of the Related Art

During the combustion of natural gas, liquefied natural gas on propane,NO_(x) is formed and emitted to the atmosphere with other combustionproducts. Because these fuels contain little or no fuel-bound nitrogenper se, NO_(x) is largely formed as a consequence of oxygen and nitrogenin the air reacting at the high temperatures resulting from thecombustion of the fuel.

Governmental agencies have passed legislation regulating the amount ofNO_(x) that may be admitted to the atmosphere by gas furnaces and otherdevices. For example, in certain areas of the United States, e.g.,California, regulations limit the permissible emission of NO_(x) fromresidential furnaces to less than 40 ng/J (nanograms of NO_(x) per Jouleof useful heat generated). Future regulations include plans to restrictNO_(x) emissions from residential furnaces and boilers to less than 15ng/J.

Gas furnaces often use a particular type of gas burner commonly referredto as an in-shot burner or two-stage burner. Such burners include aburner nozzle having an inlet at one end for receiving separate fuel andprimary air streams and an outlet at the other end through which mixedfuel and primary air discharges from the burner nozzle in a generallydownstream direction. Fuel gas under pressure passes through a centralport disposed at or somewhat upstream of the inlet of the burner nozzle.The diameter of the inlet to the burner nozzle is larger than thediameter of the fuel inlet so as to form an annular area through whichatmospheric air (a.k.a. primary air) is drawn into the burner nozzleabout the incoming fuel gas.

The primary air mixes with the fuel gas as it passes through the tubularsection of the burner nozzle to form a primary air/gas mix. This primaryair/gas mix discharges from the burner nozzle and ignites as it exitsthe nozzle outlet section forming a flame projecting downstream from aflame front located immediately downstream of the burner nozzle outletand spaced apart from an inlet of the primary heat exchanger. Secondaryair flows around the outside of the burner nozzle and is entrained inthe burning mixture downstream of the nozzle in order to provideadditional air to support combustion as the burning mixture enters theheat exchanger inlet.

In-shot burner designs cannot meet the more stringent NO_(x) emissionrequirements because of their reliance on secondary air to complete thecombustion process. The mixing of air and fuel of such systems producedunacceptably high NO_(x) emissions higher-than the future regulations.In order to comply, the current in-shot burner design is being replacedby burner designs where the air and fuel is fully premixed beforecombustion, without the use of secondary air. Instead of providing a gapbetween the burner and heat exchanger which allows for the entrainmentof secondary air, the premixed burners are coupled to the heat exchangerinlet. By eliminating the use of secondary air, the premixing of thefuel and air can be controlled and a premixed, lean mixture may be usedfor combustion which produces less NO_(x) than traditional in-shotburners.

In multi-burner applications such as a typical sectional gas furnaceseach heat exchanger is supplied hot combustion products by individualburners. Typically only one burner contains an igniter and therefore,upon ignition, the remaining burners are lit from the single burner withthe igniter. Flame carryover is the ability to transfer the flame fromone burner to the next. The current industry standard “in-shot” burneruses a small channel between burners where a small flame transfers hotgases to light each successive burner as shown in FIG. 2. This carryovermethod has proven ineffective when used in combination with premixburners disposed immediately upstream of the heat exchanger.

SUMMARY OF THE DISCLOSURE

A gas burner for low NOx gas furnaces is disclosed with improved flamecarryover for igniting one or more adjacent burners. The burnercomprises a burner tube that receives a mixture of fuel and air. Theburner tube is coupled to an outlet. The outlet includes a primaryoutlet opening which is in communication with at least one transverseslot for communicating a flame to at least one adjacent burner.

A burner assembly is also disclosed that comprises a plurality ofburners. Each burner comprises a burner tube that receives a mixture offuel and air. Each burner tube is coupled to an outlet. Each outletcomprises a primary outlet opening that is in communication with atleast one transverse slot for communicating a flame to at least oneadjacent burner.

A low NO_(x) sectional furnace is also disclosed that comprises a burnerassembly comprising a plurality of burners. Each burner comprises aburner tube that receives a mixture of fuel and air. Each burner tube iscoupled to a primary outlet opening. Each primary outlet opening is incommunication with at least one transverse slot for communicating aflame to at least one adjacent burner.

Other advantages and features will be apparent from the followingdetailed description when read in conjunction with the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosed methods andapparatuses, reference should be made to the embodiments illustrated ingreater detail in the accompanying drawings, wherein:

FIG. 1 is a perspective view of a prior art sectional gas furnace;

FIG. 2 is a partial perspective view of a prior art in-shot burnerassembly equipped with a flame carryover mechanism for use in asectional gas furnace, like the furnace illustrated in FIG. 1;

FIG. 3 is side view of a prior art lean pre-mix burner and flameretention device that are coupled to a heat exchanger section;

FIG. 4 is a front perspective view of an outlet for a disclosed pre-mix,low NO_(x) burner that includes an integrated flame carryover mechanism;

FIG. 5 is a rear perspective view of the burner outlet illustrated inFIG. 4;

FIG. 6 is a top plan view of a piece of sheet metal cut to form theburner outlet illustrated in FIGS. 4-5;

FIG. 7 is a side plan view illustrating the coupling of a disclosedburner outlet to a sectional heat exchanger; and

FIG. 8 is a partial perspective view of a disclosed burner assemblyillustrating the flame carryover mechanism.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Referring first to FIG. 1, a sectional gas furnace 10 is shown whichcomprises a burner assembly 11 with a burner box 12 that is decoupledfrom the inlets 49 of the primary heat exchanger sections, only one ofwhich can be seen at 13. The primary heat exchanger sections 13 are influid communication with corresponding condensing heat exchangersections 14 whose discharge end is fluidly connected to a collector box16 and an exhaust vent 17. In operation, a gas valve 18 meters the flowof gas to the burner assembly 11 where combustion air from an air inlet19 is mixed and ignited by an igniter assembly 21. The hot gas andsecondary air are passed through the inlets 49 of the primary heatexchanger sections 13. The primary heat exchanger sections 13 lead tothe condensing heat exchanger sections are 14, as shown by the arrows20.

The relatively cool exhaust gases then pass through the collector box 16and exhaust vent 17 before being vented to the atmosphere, while thecondensate flows from the collector box 16 through a drain line 22 fordisposal. Flow of combustion air into the air inlet through the heatexchanger sections 13, 14 and the exhaust vent 17 is controlled by aninducer fan 23. The inducer fan 23 is driven by a motor 24 in responseto signals from the integrated furnace control or IFC 29. The householdair is drawn into a blower 26 which is driven by a drive motor 27, inresponse to signals received from the IFC 29. The discharge air from theblower 26 passes over the condensing heat exchanger sections 14 and theprimary heat exchanger sections 13, in a counter-flow relationship withthe hot combustion gases to thereby heat the indoor air, which thenflows from the discharge opening 28 in the upward direction as indicatedby the arrows 15 to a duct system (not shown) within the space beingheated.

Turning to FIG. 2, a pair of-shot burners 31 illustrated that arefabricated from two half shells 32, 33. The flame retention devices areillustrated at 34. The half shells 32, 33 provide for a convenientpassageway 35 that can be used for flame carryover between the twoburners 31. Such a flame carryover construction is not suitable for lowNO_(x), lean pre-mix burners designed to meet the more stringent NO_(x)regulations of the future.

For example, turning to FIG. 3, a lean pre-mix burner 36 is illustratedas coupled to a primary heat exchanger section 13. The burner 36includes a burner tube 37 and a fuel nozzle 38. Air is drawn into theburner to 37 under the pull of the inducer fan 23 (FIG. 1) as indicatedby the arrows 39. A flame retention device 134 is illustrated at thejunction between the heat exchanger section 13 and the burner tube 37.The burner tube 37 may also include a mixer 41, which is used todecrease lean blow-off and increase the stability of the flame. Theburner tube 37 includes an outlet section 42 that is coupled to theinlet 49 of the heat exchanger section 13.

An improved outlet section 142 is provided as illustrated in FIGS. 4-5.Turning to FIG. 4, the outlet section 142 includes an elliptical primaryoutlet opening 145 that includes a pair of outwardly extendingtransverse slots 146 that extend along a minor access 147 of theelliptical opening 145. FIG. 6 provide a top plan view of a forfabricating the burner outlet 142 from a single piece of sheet metal.Specifically, the side panels 151 are connected to a top panel 152which, in turn, is connected to a front panel 153 which includes theelliptical primary outlet 145 and transverse slots 146. The front panel153 is connected to a bottom panel 154. The two front walls 155, 156 maybe connected to the inlet 49 of a heat exchanger section 13 asillustrated in FIG. 7. The sidewalls 151 may be connected to a joiningsidewalls of other burner outlets to form a burner assembly 160 asillustrated in FIG. 8.

Because the flame retainer device 134 can provide a complex flow fieldthat allows the flame to anchor to it, mesh burners like those shown at36 in FIG. 3 are typically used in single burner applications and aredesigned in such a fashion to provide a continuous burner surface.Sectional gas furnaces use multiple heat exchangers each with anindividual burner. Therefore, applying a continuous burner betweenmultiple heat exchangers will over temp both the inlet to the heatexchangers and the area between heat exchangers of the panel that theheat exchangers are mounted to. Creating a zone of lower energy releasebetween burners as illustrated in FIGS. 4-8 will mitigate over tempingwhile allowing a semi-continuous combustion surface for multi-burnerignition (FIG. 8).

While only certain embodiments have been set forth, alternatives andmodifications will be apparent from the above description to thoseskilled in the art. These and other alternatives are consideredequivalents and within the spirit and scope of this disclosure and theappended claims.

1. A burner comprising: a burner tube that receives a mixture of fueland air, the burner tube coupled to an outlet, the outlet comprising aprimary outlet opening, the primary outlet opening being incommunication with at least one transverse slot for communicating aflame to at least one adjacent burner.
 2. The burner of claim 1 whereinthe at least one transverse slot extends from the primary outlet openingand terminates short of an outlet of the adjacent burner.
 3. The burnerof claim 1 wherein the primary outlet opening is elliptical with asemi-minor axis, and the at least one transverse slot is disposed alongthe semi-minor axis of the primary outlet opening.
 4. The burner ofclaim 1 wherein the primary outlet opening is elliptical with asemi-minor axis and the outlet further comprises a pair of oppositelydirected transverse slots extending outward from the primary outletopening along the semi-minor axis of the primary outlet opening.
 5. Theburner of claim 1 wherein the primary outlet opening is elliptical andthe outlet further comprises a concave outer face through which theprimary outlet opening extends.
 6. The burner of claim 5 wherein theoutlet further comprises a pair of oppositely directed transverse slotsextending outward from the primary outlet opening along a semi-minoraxis of the primary outlet opening.
 7. The burner of claim 1 wherein theburner is coupled to an igniter.
 8. A burner assembly comprising: aplurality of burners, each burner comprising a burner tube that receivesa mixture of fuel and air, each burner tube coupled to an outlet, eachoutlet comprising a primary outlet opening, each primary outlet openingbeing in communication with at least one transverse slot forcommunicating a flame to at least one adjacent burner.
 9. The burnerassembly of claim 8 wherein each transverse slot extends from itsrespective primary outlet opening and terminates short of the outlet ofthe adjacent burner.
 10. The burner assembly of claim 8 wherein eachprimary outlet opening is elliptical and each transverse slot isdisposed along the semi-minor axis of its respective primary outletopening.
 11. The burner assembly of claim 8 wherein each primary outletopening is elliptical and each outlet further comprises a pair ofoppositely directed transverse slots extending outward from theirrespective primary outlet opening along a semi-minor axis of theirrespective primary outlet opening.
 12. The burner assembly of claim 8wherein each primary outlet opening is elliptical and each outletcomprises a concave outer face through which the primary outlet openingextends.
 13. The burner assembly of claim 12 wherein each outlet furthercomprises a pair of oppositely directed transverse slots extendingoutward from their respective primary outlet opening along a semi-minoraxis of their respective primary outlet opening.
 14. The burner assemblyof claim 8 wherein only one burner is coupled to an igniter.
 15. A lowNO_(x) furnace, comprising a burner assembly comprising a plurality ofburners, each burner comprising a burner tube that receives a mixture offuel and air, each burner tube coupled to an outlet, each outletcomprising a primary outlet opening, each primary outlet opening beingin communication with at least one transverse slot for communicating aflame to at least one adjacent burner.
 16. The furnace of claim 15wherein each transverse slot extends from its respective primary outletopening and terminates short of the outlet of the adjacent burner. 17.The furnace of claim 15 wherein each primary outlet opening iselliptical and each transverse slot is disposed along the semi-minoraxis of its respective primary outlet opening.
 18. The furnace of claim15 wherein each primary outlet opening is elliptical and each outletfurther comprises a pair of oppositely directed transverse slotsextending outward from their respective primary outlet opening along asemi-minor axis of their respective primary outlet opening.
 19. Thefurnace of claim 8 wherein each primary outlet opening is elliptical andeach outlet comprises a concave outer face through which the primaryoutlet opening extends.
 20. The furnace claim 19 wherein each outletfurther comprises a pair of oppositely directed transverse slotsextending outward from their respective primary outlet opening along asemi-minor axis of their respective primary outlet opening.
 21. Thefurnace of claim 15 wherein only one burner is coupled to an igniter.